JPH097948A - Generating method for molecular beam and molecular beam cell - Google Patents

Abstract

PURPOSE: To provide a method for generating a molecular beam capable of solving the problem of a droplet and obtaining a stable evaporation rate. CONSTITUTION: In a molecular beam cell having a crucible 11 to be filled with an evaporation source material and heating means 41 for heating the material, the means 41 comprises a first heater 41a, provided at least at the sidewall of the part of the bottom side of the crucible 11, and a second heater 41b provided at the sidewall of the part of the opening side of the crucible 11. The part of the bottom side of the crucible is heated under such a heating condition that a first temperature distribution develops, and a molecular beam is generated while heating the part of the opening side of the crucible under such a heating condition that a second temperature distribution develops.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a molecular beam in an MBE (molecular beam epitaxy) apparatus and the like, and a molecular beam cell suitable for carrying out the method.

[0002]

2. Description of the Related Art A molecular beam cell is used to generate a molecular beam in an MBE apparatus. A typical conventional molecular beam cell was as described below with reference to FIG.
However, in FIG. 3, the conventional molecular beam cell 10 and the sample side portion 30 on which a thin film is formed are shown together. This conventional molecular beam cell 10 includes a crucible 11, a heater 13 provided on the entire circumference and bottom surface of a side wall of the crucible 11, a heat insulating material 15 for preventing heat of the heater 13 from escaping to the outside, A thermocouple 17 for detecting the temperature of the crucible 11, a support 19 for supporting the crucible 11, the heater 13, the heat insulating material 15 and the thermocouple 17, and a shutter 21 attached to and detached from the opening 11 a of the crucible 11.
It was equipped with. The crucible 11 is made of a material that does not react with the vapor deposition material and has a high melting point, such as PBN (pyrolytic boron nitride). The heater 13 is composed of a heating element such as tungsten that can heat the crucible 11 to a temperature of about one thousand and several hundred degrees. The heater 13 typically has a wire shape. In that case, appropriate treatment with an insulator is performed so that the wire-shaped heaters do not come into contact with each other. The heat insulating material 15 is usually formed by winding a plate-shaped high melting point metal around the heater in multiple layers.

In a high-vacuum deposition chamber (not shown),
The crucible 11 is heated by the heater 13. Since the evaporation source material (for example, Ga) 23 contained in the crucible 11 is evaporated by this heating, a molecular beam corresponding to the evaporation source material is generated. Since this molecular beam reaches the substrate 30a in the sample side portion 30, the evaporation source material 23 is formed on the substrate 30a.
A thin film corresponding to is formed.

[0004]

However, in the conventional method for producing a molecular beam and the conventional molecular beam cell, since the crucible 11 is heated by the heaters 13 uniformly provided on the side wall and the bottom surface of the crucible 11, the opening portion of the crucible 11 is heated. The temperature of the portion close to 11a becomes lower than the other portions due to the effect of heat radiation in the opening. For this reason, a phenomenon occurs in which a large number of evaporation source material particles 25 (which are referred to as droplets) adhere to the portion of the inner wall of the crucible 11 near the opening 11a. Then, some of the droplets fly to the substrate as lumps (not in the molecular beam state),
There is a problem that it causes defects in the thin film to be formed.

In order to prevent this, the inventor of the present application, as shown in FIG. 4, provided the heater 13 only around the side wall of the opening 11a side of the crucible 11 (the upper part of the crucible 11). A molecular beam cell 10a against droplets was produced and an experiment was tried. According to this molecular beam cell 10a,
I was able to prevent the generation of droplets, but the following new problems arose. That is, the opening 11a of the crucible 11
In the case of the molecular beam cell 10a in which the heater 13 is provided only around the side wall of the side portion (the upper portion of the crucible 11), the crucible 1
Since the temperature gradient between the upper part and the lower part of 1 becomes large, (a)
As the film formation progresses and the liquid level 23a of the evaporation source material 23 decreases, the evaporation amount per unit time decreases, and (b) to prevent this, the power supplied to the heater 13 is changed. When it does, the problem that control is difficult arises. This will now be described in some detail with reference to the schematic model of FIG. Here, FIG. 5 is a diagram schematically showing the temperature distribution on the line connecting the opening and the bottom of the crucible 11 in the molecular beam cell 10a shown in FIG.

In the case of the molecular beam cell 10a in which the heater 13 is provided only around the side wall of the opening 11a side of the crucible 11 (upper part of the crucible 11), the upper part of the crucible 11 naturally has a higher temperature. The temperature is only high when the temperature is high, and while the heater 13 is not present (at the point P in FIG. 5) toward the bottom surface of the crucible, the temperature only decreases. For this reason, when the liquid level of the evaporation source material passes from point P above the point P to the bottom side of the crucible, the amount of evaporation decreases. Therefore, the problems (a) and (b) above tend to occur as the evaporation source material is used in a large amount and the film formation is performed for a long time.

There is a demand for a molecular beam generation method and a molecular beam cell which can solve the problem of droplets and can secure a stable vapor deposition rate.

[0008]

Therefore, according to the first invention of this application, in heating the crucible containing the evaporation source material by the heating means to generate the molecular beam corresponding to the evaporation source material, The molecular beam is heated while heating the portion on the bottom side of the crucible under the heating condition that provides the first temperature distribution, and the portion on the opening side of the crucible under the heating condition that provides the second temperature distribution. Is generated.

Here, the first temperature distribution is a distribution in which the evaporation amount of the evaporation source material per unit time can be a predetermined amount,
It is preferable that the second temperature distribution is a distribution that can prevent the generation of droplets. The respective specific profiles of the first and second temperature distributions may be determined, for example, experimentally in consideration of the shape and size of the crucible, the type of evaporation source material, etc. (in the second invention. the same.). Although not limited to this, as for the heating condition, the temperature distribution on the opening side of the crucible, that is, the second temperature distribution, is higher than the temperature distribution on the bottom side of the crucible, that is, the first temperature distribution. The distribution is set (same in the second invention). Further, it is considered that the amount of the evaporation source material used is preferably such that the liquid surface of the evaporation source material is located within the first temperature distribution (the same applies to the second invention).

Further, according to the second invention of this application, in a molecular beam cell comprising a crucible for containing an evaporation source material and a heating means for heating the crucible, the heating means is provided at least on a bottom side portion of the crucible. A first heating part provided on the side wall for forming a first temperature distribution; and a second heating part provided on the side wall on the opening side of the crucible for forming a second temperature distribution. It is characterized by including.
In addition, in this second invention, the meaning of "at least" at least on the side wall of the bottom side portion of the crucible is whether the second heating portion is provided on the bottom surface of the crucible as an extension or not. Invention is meant to include.

Further, in carrying out the second aspect of the invention, radiation of heat emitted from both heating portions is applied to a portion of the side wall of the crucible which is a boundary between the first heating portion and the second heating portion. It is preferable to provide a heat shield for suppressing mutual interference due to.

[0012]

According to the structure of the first aspect of the present invention, the molecular beam is generated while actively heating the bottom side portion and the opening side portion of the crucible so that the temperature distributions meet the respective purposes. . In the case of the configuration of FIG. 5, the present invention and the technique using FIG. 5 are different from the point that the bottom side portion of the crucible is heated only subordinately and is not actively heated.

Further, according to the structure of the second invention, since the predetermined first heating portion and the predetermined second heating portion are provided, the bottom side portion and the opening side portion of the crucible are positively provided respectively. The heating can be easily performed so that the temperature distribution has a purpose.

In the second aspect of the present invention, which is provided with the heat shield, the independence of the first heating section and the second heating section is further increased. A second temperature distribution can be formed.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the inventions of this application will be described below with reference to the drawings. However, the drawings used for the description schematically show the dimensions, shapes, and arrangement relationships of the respective constituents to the extent that the present invention can be understood. Further, in each of the drawings used for description, the same constituents and the same constituents as those in the related art are denoted by the same reference numerals and the same reference numerals as those used in FIGS. 3 and 4.

FIG. 1 is an explanatory view of the first invention and the second invention, and is a side view showing a molecular beam cell 40 of an embodiment of the second invention, in which a part thereof is cut away.

The molecular beam cell 40 of this embodiment is a crucible 1
1, a first heating portion 41a provided on at least a side wall (only a side wall in the illustrated example) of a bottom side portion of the crucible 11 and the crucible 1
The heating means 41, which is provided on the side wall of the opening 11a side of the first heating portion 41b for forming the second temperature distribution, and the heat of the heating means 41 escape to the outside. A heat insulating material 15 for preventing, and a first thermocouple 17a for detecting the temperature of the bottom side portion of the crucible 11,
A second thermocouple 17b for detecting the temperature of the portion of the crucible 11 on the side of the opening 11a, and a support 19 for supporting the crucible 11, the heating means 41, the heat insulating material 15 and the thermocouples 17a, 17b. , The shutter 21 that is attached to and detached from the opening 11 a of the crucible 11, and the first heating unit 41 a and the second heating unit 41 of the side wall of the crucible 11.
A heat shield portion 43 for suppressing mutual interference due to radiation of heat generated by both heating portions 41a and 41b is provided at a portion corresponding to the boundary with b.

Here, the crucible 11, the heat insulating material 15, the first thermocouple 17a, the second thermocouple 17b, the support 19 and the shutter 21 are included in the conventional molecular beam cell described with reference to FIG. It can be composed of the same ones. However, regarding the thermocouples 17a and 17b, the first thermocouple 17a
Is a position suitable for detecting the temperature of the bottom side portion of the crucible 11 (here, a position in contact with the bottom surface of the crucible), while the second thermocouple 17b is for detecting the temperature of the opening portion 11a side of the crucible 11. It is arranged at a suitable position so that the respective tip portions are in contact with each other. But in some cases, thermocouples
Only one of the first and second, and preferably only the first thermocouple 17a for the bottom side may be used. Even in such a case, both heating parts 41a and 41b can be controlled so as to obtain a temperature distribution practically desired (details will be described later with reference to FIG. 2).
This will be described with reference to FIG. ).

The first heating portions 41a and 41b are not particularly limited as long as they can form the first temperature distribution and the second temperature distribution, respectively. In this embodiment, however, as shown in FIG. ) And (B) will be described. In addition, in FIG. 2, in each aspect,
Crucible 11 and first and second heating units 41a and 41b
And a temperature control device 4 which is another component of the heating means 41.
It is a figure showing the relation between 1c and thermometer 41d, and heat shield part 43.

First, in the first mode shown in FIG. 2A, a heating means 41 is constructed by winding a series of linear heaters on the side wall of the crucible 11. However, when winding a series of linear heaters on the side wall of the crucible 11, the density of winding the linear heater on the side wall on the bottom side of the crucible 11 and the crucible 1
The density of winding the linear heater on the side wall on the side of the opening 11a of No. 1 differs depending on the predetermined conditions, and the first heating unit 41a is formed on one side of the heaters having the different densities. On the other hand, the 2nd heating part 41b is comprised. The ratio of the first heating portion 41a to the second heating portion 41b with respect to the entire height of the crucible 11 is determined by the degree of cooling due to the opening 11a of the crucible 11, The amount of evaporation source material to be placed in the crucible 11 and the like are mainly considered and determined (the same applies in the second embodiment below). When the temperature distribution on the bottom side portion of the crucible 11 is made lower than the temperature distribution on the opening side portion, the heater winding density on the bottom side is set to be lower than that on the opening side. . Further, in the case of this embodiment, the temperature control in the case of this first mode is performed by the first and second thermometers 41d.
Of either of the thermocouples 17a and 17b (preferably the first thermocouple 17a for the bottom side) is connected, and the thermometer 41d outputs the output of the connected thermocouple to the temperature control device 4
1c, and the temperature control device 41c controls the temperature based on the input.

In the second embodiment shown in FIG. 2B, linear heaters are provided on the side wall of the bottom side of the crucible 11 and the side wall of the crucible 11 on the opening 11a side. The first heating part 4 is wound separately and is heated by the former heater.
1a, and the second heater 41b by the latter heater
Is composed. In the case of this embodiment, the temperature control in the case of the second mode is such that two systems of the temperature control device 41c and the thermometer 41d are provided, one system controls the first heating unit 41a, and the other system controls. In the system, the second heating unit 41
Control b. In the second aspect, the first heating unit 41
There is an advantage that each of the a and the second heating unit 41b can be controlled independently.

In both the first and second aspects, the number of windings, the winding position, and the density of the linear heater are set to be suitable conditions according to the design.

Further, the heat shield portion 43 includes both heating portions 41a,
It is not particularly limited as long as it can suppress mutual interference due to radiation of heat generated by 41b. In the case of this embodiment, the heat shield 43 is configured by arranging a reflector made of a refractory metal such as tungsten around the side wall of the crucible. The number of reflectors is determined according to the design.

In the molecular beam cell 40 described with reference to FIGS. 1 and 2, the crucible 11 is heated by the first heating section 41a.
Of the crucible 11 is heated by the second heating portion 41b while heating the bottom side portion of the crucible 11 under the heating condition that the first temperature distribution is obtained.
The molecular beam can be generated while heating the portion on the side of the opening portion 11a under the heating condition that provides the second temperature distribution. Therefore,
The bottom side of the crucible has a temperature distribution that allows the evaporation amount of the evaporation source material per unit time to be a predetermined amount (constant amount), and the opening side of the crucible has a temperature distribution that can prevent generation of droplets. The molecular beam can be generated while heating under each of the heating conditions described below.

[0025]

As is apparent from the above description, according to the molecular beam producing method of the first invention of the present application, the bottom side portion and the opening side portion of the crucible are positively purposed respectively. The molecular beam is generated while heating so that the temperature distribution matches. For this reason, the temperature of the evaporation source material in the crucible can always be kept at a uniform temperature, so the evaporation amount of the material per unit time can be made constant, while the temperature on the opening side of the crucible prevents the generation of droplets. It can be done at any temperature.
Therefore, vapor deposition can be performed without generating droplets and at a stable vapor deposition rate.

Further, according to the structure of the second invention, since the predetermined first heating portion and the predetermined second heating portion are provided, the bottom side portion and the opening side portion of the crucible are positively and respectively provided. The heating can be easily performed so that the temperature distribution has a purpose. Therefore, the implementation of the first invention is facilitated.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment of the first and second inventions, and is an explanatory view of a molecular beam cell of the embodiment.

FIG. 2 is an explanatory diagram of an embodiment of the first and second inventions, and is an explanatory diagram of some specific examples of heating means.

FIG. 3 is an explanatory diagram of conventional technology and problems.

FIG. 4 is an explanatory diagram of a conventional technique and a problem.

FIG. 5 is an explanatory diagram of a problem.

[Explanation of Codes] 11: Crucible 15: Heat Insulating Material 17a: First Thermocouple 17b: Second Thermocouple 19: Support 21: Shutter 40: Molecular Beam Cell of Example 41: Heating Means 41a: First Heating unit 41b: Second heating unit 43: Heat shield unit

Claims (5)

[Claims] 1. When a crucible containing an evaporation source material is heated by a heating means to generate a molecular beam, a bottom side portion of the crucible is heated under a heating condition so as to have a first temperature distribution, and A method for producing a molecular beam, wherein the molecular beam is produced while heating a portion of the crucible on the opening side under a heating condition that provides a second temperature distribution. 2. The method for producing a molecular beam according to claim 1, wherein the first temperature distribution is a distribution in which the evaporation amount of the evaporation source material per unit time can be a predetermined amount, and the second temperature distribution is A method for producing a molecular beam, which has a distribution capable of preventing the generation of droplets. 3. A molecular beam cell comprising a crucible containing an evaporation source material and a heating means for heating the crucible, wherein the heating means is provided on at least a side wall of a bottom side portion of the crucible.
A first heating part for forming a temperature distribution of the crucible and a second heating part for forming a second temperature distribution provided on the side wall of the opening side of the crucible. Molecular beam cell characterized by. 4. The molecular beam cell according to claim 3, wherein the first temperature distribution is a distribution that allows a predetermined amount of evaporation of the evaporation source per unit time, and the second temperature distribution is of droplets. A molecular beam cell having a distribution capable of preventing generation. 5. The molecular beam cell according to claim 3, wherein both heating portions emit light to a portion of a side wall of the crucible that is at a boundary between the first heating portion and the second heating portion. A molecular beam cell comprising a heat shield for suppressing mutual interference due to heat radiation.